1. Field of the Invention
The present invention relates to a scroll-type fluid machine. More specifically, the present invention relates to a mechanism for canceling a centrifugal force applied to an orbiting scroll, and a seal mechanism and a relief mechanism at a gap between the spiral walls of orbiting and fixed scrolls in their radial direction.
2. Discussion of Background
Referring now to FIG. 6, there is shown the operating principal of a scroll-type fluid machine. Reference numeral 10 designates a fixed scroll. Reference numeral 11 designates an orbiting scroll. Reference character C designates a compression chamber which is defined between both scrolls 10 and 11. Reference numeral 101 designates a discharge port. The fixed scroll 10 and the orbiting scroll 11 have base plates, respectively, each of which has one side provided with a spiral wall having a similar shape. Each spiral wall has an involuted shape or a combination of circular arcs, which is well known. When the scroll-type fluid machine is used as a compressor, the fixed scroll 10 is fixed in terms of special relations, and the orbiting scroll 11 is combined with the fixed scroll 10 as shown in FIG. 6, and carries out such turning movement or orbital movement that the oribiting scroll 11 does not change its posture in terms of space. The orbital movement is made with a predetermined crank radius (orbiting radius) as shown in at 0.degree., 90.degree., 180.degree. and 270.degree. in FIG. 6. As the movement of the orbiting scroll 11 progresses, the area of the compression chamber C, which is defined between the fixed scroll 10 and the orbiting scroll 11, and which is in the form of crescent, is gradually decreased, so that a gas which entrapped in the compression chamber C is compressed, and is discharged from the discharge port 101. This is the operating principal of the scroll-type fluid machine.
Referring now to FIG. 7, there is shown an axial sectional view showing a compressor wherein a conventional scroll-type fluid machine is utilized. Reference numeral 10 designates a fixed scroll. Reference numeral 11 designates an orbiting scroll which has an orbiting shaft 112 on the back. Reference numeral 12 designates a driving shaft which has an orbiting bearing hole 121 eccentrically formed therein and is constructed with a counter-weight 122 into a single unit, the orbiting shaft 112 being fitted in the orbiting bearing hole 121 through an orbiting bearing 23. Reference numeral 13 designates an electric motor rotor which is constructed with the driving shaft 12 into a single unit. Reference numeral 14 designates an electric motor stator. Reference numerals 15 and 16 designates bearing supports. Reference numeral 17 designates a shell. Reference numeral 18 designates an intake tube which is attached to and through the shell 17. Reference numeral 19 designates a discharge tube which is attached to and through the shell 17 as well. Reference numeral 20 designates a discharge muffler which is arranged at the leading end of the discharge tube 19. Reference numeral 21 designates a check valve which is arranged at a discharge port 101. Reference numeral 22 designates an Oldham ring which is used to prevent the orbiting scroll 11 from rotating on its axis and to keep an angular position of the orbiting scroll 11 with respect to the fixed scroll 10. Reference numeral 24 designates a main bearing which is arranged to decrease the friction between the driving shaft 12 and the bearing support 16. Reference numeral 25 designates a subbearing which is used to support the driving shaft 12 at the side of the electric motor. Reference numeral 26 designates an annular thrust bearing to which the internal pressure in the compression chamber C and the tare of the orbiting scroll 11 are applied. Reference numeral 27 designates tipseals which are fitted in tipseal grooves in end surfaces of the spiral walls of the scrolls 10 and 11. Reference numeral 28 designates a foaming prevention plate. Reference numeral 29 designates a counter-weight which is mounted to the lower end of the rotor 13. Reference numeral 30 designates a lubricating oil pump which is attached to the lower end of the driving shaft 12.
Next, the operation of the scroll-type compressor shown in FIG. 7 will be explained. When the electric motor stator 14 is energized, the electric motor rotor 13 produces torque to rotate with the driving shaft 12. As a result, the torque is transmitted to the orbiting shaft 112 through the orbiting bearing 23 which is fitted in the orbiting bearing hole 121. The orbiting scroll 11 carries out orbiting movement without rotating on its own axis while being guided by the Oldham ring 22. In this way, the compression operation as shown in FIG. 6 is made. The tipseals 27 which are arranged at the leading edge of the spiral walls of both scrolls 10 and 11 seal gaps between the scrolls in their axial direction to prevent a gas from leaking in a radial direction from a higher pressure compression chamber C to a lower pressure compression chamber C. The gas which has flowed into the shell 17 through the intake tube 18 cools the electric motor rotor 13 and the electric motor stator 14 and the like. After that, the gas entrapped in the compression chamber C is compressed there, and is discharged from the discharge tube 19 through the discharge port 101.
In the conventional scroll-type compressor described above, the orbiting scroll 11 is eccentrically arranged with respect to the driving shaft 12. Rotary machines having such arrangement require that the counter-weight 122 be provided to cancel a centrifugal force which is applied to the eccentric portion. It is conventional that the counter-weight 122 is attached to the driving shaft 12 or the electric motor rotor 13 because the counter-weight 122 must rotate in phase with the eccentric portion and about the rotational center of the shaft in terms of its function.
Referring now to FIG. 8, there is shown an enlarged view of the essential parts of the compressor shown in FIG. 7. A centrifugal force which is generated at the orbiting scroll 11 is transmitted to the driving shaft 12 through the orbiting bearing 23, and is canceled by the counter-weight 122 which is constructed with the driving shaft 12 in a single unit. It means that the orbiting bearing 23 works while being subjected to a centrifugal load from the orbiting scroll 11, and that the centrifugal load is relevant to bearing loss of the orbiting bearing 23. When the centrifugal force is increased due to a high speed operation, the center of the orbiting shaft 112 has greater deviation in the orbiting bearing 23 in a direction where the orbiting radius increases. As a result, the side surfaces of the spiral wall of both scrolls 10 and 11 start to touch with each other to a large extent. Once the side surfaces of the spiral walls have started to touch to such a large extent, the centrifugal force acts against the side surface of the spiral walls to produce sliding loss on the side surfaces of the spiral wall. Because the coefficient of friction of the side surfaces is greater than that of the orbiting bearing 23, the sliding loss on the side surfaces is great. In addition, if an abnormal high pressure is generated in the compression chamber due to liquid compression or the like, a load due to such high pressure can be applied to the bearing to damage it since it is impossible to form a gap through which the high pressure is relieved.
As explained above, the conventional technique wherein the fixed crank having an invariable orbiting radius is used to mount the counter-weight 122 to the driving shaft 12 involves three problems;
1 a centrifugal load increases bearing loss at the orbiting bearing 23 under normal operations.
2 sliding loss becomes great at the side surfaces of the spiral walls of both scrolls 10 and 11 when the side surfaces of the spiral walls touch each other under high speed operations.
3 there is no relief function against abnormal internal pressures.
In order to obviate the problem 2, a so-called swing link system has been proposed wherein a mechanical link unit having flexibility in a radial direction is arranged between a driving shaft and an orbiting scroll, and wherein a counter-weight is mounted to the link unit. Referring now to FIGS. 9(A) and 9(B), there is shown an example of the swing link system disclosed in e.g. Japanese Examined Patent Publication No. 19875/1983. FIG. 9 (A) is a vertical sectional view showing the essential parts of the system. FIG. 9 (B) is a partial horizontal sectional view of the essential parts. As shown in these Figures, a driving shaft 12a is rotatably supported by a bearing support 16a through a ball bearing 24a. A driving pin 42a is uprighted at an eccentric position on top of the driving shaft 12a. About the center O.sub.3 of the driving pin 42a is rotatably arranged a bushing 41a which in turn has its periphery provided with a boss 111a through a needle bearing 23a, the boss 111a projecting from the lower end of an orbiting scroll 11a. In addition, between the bearing support 16a and the orbiting scroll 11a is provided a rotation preventing mechanism 26a. A counter-weight 411a is formed with the bushing 41a in one unit. In this system, the rotation of the driving shaft 12a is transmitted to the orbiting scroll 11a through the driving pin 42a, and the bushing 41a and the needle bearing 23a. The orbiting scroll 11a carries out orbiting movement while it is prevented from rotating by the rotation preventing mechanism 26a. In this case, the crank radius (orbiting radius) is the distance Rr from the center O.sub.1 of the driving shaft 12a to the center of the orbiting scroll 11a or the center O.sub.2 of the busing 41a. A centrifugal force Fc which is caused at the orbiting scroll 11a is canceled by the counter-weight 411a which is formed with the bushing 41a in one unit. As a result, where a circumferential component of a gas force acting on the orbiting scroll 11a at angle .theta. is defined as F.sub.g .theta., and a radial component of the gas force is defined as F.sub.gr, the force which is defined by the equation, F.sub.s =F.sub.g .theta..multidot.tan .phi.-F.sub.gr, draws the link mechanism between the centers O.sub.2 and O.sub.3 in a direction wherein the crank radius R.sub.r increases. The force is a pressing force which acts between the side surfaces of the spiral walls of a fixed scroll and the orbiting scroll 11a because the force F.sub.s is supported at the contacting points of both spiral walls.
Although the swing link system causes the spiral walls of both scrolls to be in touch with each other at all times, the force which is supported by the side surfaces of both spiral walls is not dependent on the revolution because the force is not related to centrifugal force. As a result, the sliding loss at the side surfaces of both spiral walls will not increase even when a high speed operation is made. However, the centrifugal force which is caused at the orbiting scroll 11a is balanced by the counter-weight 411a which is formed with the bushing 41a in one unit, and the problem of item 1 is not overcome because such swing link system is not different from the device of FIGS. 7 and 8 in that a centrifugal load is applied to the needle bearing 23a which acts as an orbiting bearing between the two parts 41a and 11a. In addition, when an abnormal high pressure occurs, the gap between both scrolls in their radial direction is sealed to prevent the pressure from escaping through the gap for relief because the pressing force against the side surfaces of both scrolls derives from the pressure of the gas. It means that the problem pointed out in the above mentioned item 3 is not overcome.
As discussed above, although the conventional scroll-type fluid machines can prevent sliding loss between the side surfaces of the spiral walls of a fixed scroll and an orbiting scroll at a high speed operation from increasing, the bearing loss which is caused by the centrifugal load acting on a sliding bearing portion can not be restrained from increasing, and pressure relief can not be made when an abnormal high pressure is caused.